Food service and other passenger services in passenger transport vehicles (such as aircraft, ships, buses, trains, and any other passenger transport vehicles), causes waste water and material to accrue. This waste water often includes leftover portions of beverages, water from the lavatory, and so forth. A specific form of waste water is gray water. Gray water is “used” water that drains from drinking water systems, from wash basins during hand washing, material poured down a galley sink, or any other instance in which water is soiled or loaded with waste (e.g., soaps, detergents, soils from hand washing). Gray water typically does not include contaminants such as septic wastes (water containing septic waste is generally referred to as “black water”).
Most large passenger transport vehicles are equipped with a gray water system and a waste water system for collecting, storing and ultimately disposing of gray water and other waste water, such as black water. For example, aircrafts typically have a vacuum disposal system that applies a vacuum to suck waste water from toilets and/or sinks into an on-board waste water storage tank. The suction is generated either by the pressure differential between the pressurized cabin and the reduced pressure outside of an aircraft at high flight altitudes or by a vacuum generator at ground level or at low flight altitudes.
Currently, according to current health standard guidelines for airlines, black water is vacuumed away to a septic tank on the aircraft, and gray water is vacuumed away to be discharged in a separate tank or outside the aircraft. Public health rules do not allow gray water and black water to be disposed of in the same tank. This is primarily because, if a back-up were to occur, sewage would be expelled from galley and lavatory sinks, as well as toilets, which could create a myriad of health problems. Accordingly, separate disposal and discharge of gray water can create challenges. First, if gray water is disposed outside the aircraft, it needs to be heated because aircraft travel at such high altitudes where the air is so cold, that discharging gray water at room temperature would cause it to freeze immediately. Accordingly, aircraft are equipped with drain masts that heat gray water prior to its discharge. This uses extra energy, adds to maintenance issues (e.g., clogs often form and need to be removed), and can cause safety problems on the ground if the drain masts are not turned off (e.g., extremely hot liquids can be discharged from a plane on the ground and scald a worker standing below the plane). Second, disposing gray water outside the aircraft often causes the material to “paint” the side of the plane (consider wine and orange juice being discharged outside a plane and leaving a long, unsightly streak). This adds to maintenance and cleaning costs and could tarnish an airline's reputation for being professional and well-maintained. Third, some airports will not allow gray water to be deposited on their runways, causing airlines to find alternate solutions to outside disposal. Fourth, depositing wastes outside an aircraft that are contaminated with detergent and other soils can be an environmental hazard. Accordingly, alternate solutions for disposing of gray water are needed. Providing a separate tank for gray water is not an economical solution.
Currently, most commercial aircraft are equipped with galley and lavatory sinks. These sinks are typically intended for the disposal of fluid waste, such as excess beverages, water from melting ice, soiled water from hand washing, and so forth. They are connected to small diameter drain lines (which can easily back up if clogged) and terminate at the aircraft drain mast for exhaustion to the atmosphere. In addition to the disposal problems described above, these sink systems are typically unable dispose of a slurry of liquid and solid waste material, which commonly accumulate (e.g., coffee grounds or other solid/liquid mixed waste products).
One response to the disposal challenges presented by gray water has been to provide a food waste disposal system that includes a galley sink system based on existing aircraft vacuum toilet designs. One problem with these designs is that they can be quite loud. A flushing sound is created when the flush valve opens; the differential pressure is what forcefully draws the waste down the drain. If such systems are incorporated into a galley sink (which is not necessarily behind a closed door, but in a passageway near aisles where passengers sit), a lid can be provided, but that can be inconvenient and not entirely effective for noise reduction.
Accordingly, it is desirable to provide a galley waste disposal system, and particularly, a system and method for removal of gray water from passenger transport vehicles such as aircraft, that can remove liquid waste (as well as liquid waste that may be partially mixed with solid waste), and that can conduct this removal in a discrete, relatively quiet, and environmentally friendly manner. It is also desirable to provide a system and method for storing gray water in the black water (or septic) tanks that are on-board an aircraft that includes a no-fail valve that will prevent any back up of the tank into sinks or basins that receive gray water.